1. Field of the Invention
The present invention relates to a printing station utilized in apparatus such as a printer, facsimile or copying machine, wherein a cut sheet of paper is used as a recording medium and the cut sheet is fed continuously to the printing station and printed thereon with a high speed. More particularly, the invention relates to a control method of stopping plural transport means when a feed failure of the cut sheet is detected during operation.
In the printing station with a high speed, a cut sheet is separated from stacked sheets provided by a cassette one by one. The cut sheet is transferred by a transport means in a feeding unit even when the previously transferred sheet is still remaining and moving in a printing and ejecting units. Therefore, the sequence to stop each transport means at a proper time is an important problem when the cut sheet is jammed.
2. Description of the Prior Art
FIG. 1 shows outline structure of the conventional printing station comprising a feeding unit 1, a printing unit 2 and an ejecting unit 3. Cut sheets PP are provided and stacked in a hopper 10, usually in a sheet cassette. Each sheet is separated one by one by a rotation of a separating roller 11, and is transferred by a movement of a feed roller pair 12 and a register roller pair 13 into printing unit 2.
In a printing unit 2, a latent image of printing information is formed by an optical means (not shown) on a photoconductive drum 20, and is developed by toner powder during a rotation thereof. The developed toner image is transferred onto the contacting and moving sheet and is fixed by a heat roller (not shown).
The printed sheet is transferred into an ejecting unit 3, and two roller pairs 30 and 31 eject the sheet into a stacker (not shown). When a cut sheet is jammed at a specific roller position in the printing station, the sheets are jammed one after another at this position. This causes an overload to the main motor which drives all transport means, finally resulting in a standstill of operation. In the prior art, therefore, all movements of the printing station are stopped as soon as the sheet jamming is detected by a sensor.
Where the printing speed is not too fast such that the next sheet is transported after the previous sheet is ejected from the printing station, the above method of stopping all movements of transport means in the printing station does not become a serious problem. However in the high speed printing station of FIG. 1, the cut sheet is separated and transferred to the position of a register roller pair 13 provided just before the inlet of the printing unit 2 and waits for a while in order to synchronize the sheet's movement with printing operation. This movement of separating and transferring the sheet starts while the previous sheet is still in a printing process. If a sheet jamming is detected in the feeding unit 1 and all transport means in the printing station are stopped, the previous sheets, which are still remaining in the printing and ejecting units 2 and 3 cannot be used again, because the printing quality thereon becomes inferior, and moreover, the sheet during the fixing operation is overheated and scorched by the heat roller. The fixing unit is contaminated by toner powder and good quality of printing cannot be expected even when the operation is resumed after removal of the jammed sheet.